You'd be surprised at what a good shop can do with a set of junk (looking) heads. I've seen where guys have taken some bad looking stuff and had them re-finished and no problems at all. It's actually pretty common in the racing world. From the looks of the plug, something detonated pretty good. Was it the #2 cylinder (on the back)? That tends to be the culprit when all hell is about to break loose for some reason, and I really don't know why. Chances are too, that the piston could have been damaged for a long time before it decided to let go.
If you do decide to go with the L26, you might want to start out with a good ol' 3.8 on that GenV and put some good timing into it. You could probably see some good gains with the higher compression and the setup you are running now.